The study of the phenomenon of resistance of the Chinese hamster to Trichinella spiralis (muscle phase) is in progress. The non-resistant golden hamster is being used, where appropriate, as a comparative host in studies on responses to this infection. Immune responses (humoral and cellular) to the infectious process are being sequentially evaluated in terms of similarities and differences between Chinese (resistant) and golden (non-resistant) hamsters. Although it is evident that specific acquired immunity is an effector mechanism of resistance in the Chinese hamster, the possibility that earlier, physiological events which occur in the affected muscle contribute to its efficacy is being explored. Attention is focused on behavior of lysosome related enzymes in both hosts during the infectious process. Agents (e.g., chloroquine) which affect stability of lysosomal membranes are being employed to determine their effects on resistance as measured by recoveries of carcass larvae from treated, infected animals.